Composites of poly(L‐lactide) with hemp fibers: Morphology and thermal and mechanical properties

Abstract

Composites of poly(L-lactide) (PLA) with hemp fibers (Cannabis sativa), prepared by batch mixing and plasticized with poly(ethylene glycol) (PEG; weight-average molecular weight ¼ 600 g/mol), were examined by polarized optical microscopy, scanning electron microscopy, wide-angle X-ray scattering, differential scanning calorimetry, thermogravimetric analysis, and mechanical tests. The properties of both fully amorphous and semicrystalline samples of PLA/hemp and PLA-PEG/hemp composites were analyzed as a function of the fiber amount. The cold-crystallization kinetics of PLA in amorphous composites were investigated under isothermal conditions within the range of 70-1308C. For PLA/hemp samples, the bulk crystallization rate displayed a maximum near 1108C, whereas for plasticized samples, a higher and almost constant crystallization rate was observed over the entire temperature range, independently of the hemp amount. The kinetics were then analyzed on the basis of the Avrami model. The effect of fibers on the growth morphology of PLA spherulites, as well as the influence of the plasticizer on the melting behavior of PLA crystals and their reorganization during heating, was also examined. The thermogravimetric analysis of the composites, carried out in both nitrogen and air, showed that the degradation process of fiber-filled systems started earlier than that of plain PLA, independently of the presence of the plasticizer. Mechanical tests showed that the modulus of elasticity of the composites markedly increased with the hemp content, reaching 5.2 GPa in the case of crystallized PLA reinforced with 20 wt % hemp, whereas the elongation and stress at break decreased with an increasing amount of fiber for all examined systems. Plasticization with PEG did not improve the tensile properties of the composites.

Characterisation of low-odour emissive polylactide/cellulose fibre biocomposites for car interior

“…c) DSC thermograms of dPLA pellets, PLA10F05Ex-C pellets and PLA10F05Ex-CI bars endotherm peak is due to the rearrangement of the instable crystalline form (*+) of PLA into the stable crystalline form (*). The shoulder on the endotherm, already reported for neat PLA [33] and PLA/20 wt% hemp [28], can be explained by three main mechanisms, namely melt-recrystallization, dual lamellae population [28], and dual crystal structure [33]. The DSC thermograms of biocomposites with or without absorbent agent (Figure 5b and 5c) are similar to those of neat PLA.…”

“…seat backs, side and back doorpanels, boot liners [17,19,24]. In the case of PLA, a wide range of vegetal fibres (flax [25,26], kenaf [27], hemp [28], wood flour or pulp [29,30]) was used in order to adapt the properties of PLA-biocomposites to the technical specifications for automotive applications. Generally, the mechanical properties of the matrix are greatly improved by incorporating natural fibres, whatever their type [29,[31][32][33][34].…”

Functionalization, Compatibilization and Properties of Polyolefin Composites with Natural Fibers

“…An increased thermal stability was found in PP composites with GMA modified hemp; moreover, marked changes in the morphology and overall crystallization rate of PP were observed in these composites due to the enhanced nucleating effect on the fiber surface. For all examined materials, the mechanical analysis showed that tensile modulus and elongation at break are significantly affected by the type and amount of fiber (aspect ratio: [10][11][12][13][14][15][16][17][18][19][20], as are affected by the structure (and concentration) of compatibilizer. In particular, the addition of functionalized polyolefins (PP-g-GMA, PS-co-MA) resulted in an increased stiffness owing to the improved fiber-matrix adhesion.…”

“…Moreover, as shown in Figure 5, the observed values of the Avrami exponent n indicated that the nucleation process of the polymer crystals was affected by the fibers. Since the overall crystallization rate of the polyolefin is related to the spherulite growth rate, and the number of primary nuclei per unit volume [18], and as the growth rate is not affected by the fiber content, the increase of the overall crystallization rate in the composites can be ascribed to the increased crystal nucleation density on the fiber surface [19,20]. This effect was more marked for composites with Hemp-GMA mainly as a consequence of the enhanced fiber-matrix interactions.…”

Twin-screw extrusion impact on natural fibre morphology and material properties in poly(lactic acid) based biocomposites

“…PLA-based biocomposites have been widely studied and several types of vegetal fibres have been incorporated (Faruk et al, 2012). Fibres coming from wood (Huda et al, 2006;Sykacek et al, 2010), flax (Oksman et al, 2003), hemp (Masirek et al, 2007), kenaf (Ogbomo et al, 2009) and jute (Plackett, 2004) have been tested among others. Lezak et al (2008) and Nyambo et al (2010) also studied the incorporation of various agricultural residues.…”